Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$177.55	7.722%	$191.2604	$191.26	$191.25	$191.30
Purchase #2	$91.76	12.260%	$103.0098	$103.01	$103.00	$103.00
Purchase #3	$226.65	8.237%	$245.3192	$245.32	$245.30	$245.30
Purchase #4	$66.66	9.599%	$73.0587	$73.06	$73.05	$73.10
Purchase #5	$153.89	12.872%	$173.6987	$173.70	$173.70	$173.70
Purchase #6	$156.80	6.687%	$167.2852	$167.29	$167.30	$167.30
Purchase #7	$133.25	9.810%	$146.3218	$146.32	$146.30	$146.30
7 purchase totals =	$1,006.56		$1,099.9538	$1,099.96	$1,099.90	$1,100.00